This proposal responds to PA-06-278 (Neurotechnology Research, Development, and Enhancement) which calls for "significant enhancement of existing technologies ... to study the brain or behavior in basic or clinical research." We present a novel device design that substantially expands the functionality of transcranial magnetic stimulation (TMS) as a noninvasive probe of brain function with therapeutic potential by introducing continuous user-control of pulse shape. TMS modulates brain activity through the induction of cerebral currents by brief magnetic pulses. TMS has demonstrated significant antidepressant effects, but the dosing parameters associated with the best clinical outcome have yet to be identified and optimized. Although neural response is known to be highly sensitive to the shape of the stimulating pulse, existing TMS devices allow only limited control over stimulus waveform. Conventional TMS devices induce sinusoidal-exponential cerebral current pulses, while studies suggest that rectangular pulses will be more efficient. Further, high-frequency TMS devices used in clinical applications induce bidirectional current flow, while research suggests that unipolar currents would be more effective. Finally, pulse width is known to influence the efficiency of stimulation, but this parameter cannot be controlled in conventional TMS devices. We aim to design, simulate, implement, bench test and characterize a novel TMS device with controllable pulse shape (cTMS), capable of inducing approximately rectangular, predominately unipolar cerebral currents with controllable pulse width and shape. The cTMS device switches the stimulating coil between a positive and a negative capacitor bank, using newly available high-power semiconductor devices. We present simulations supporting the feasibility of the cTMS system, and the increased efficiency of rectangular pulses. The first TMS device with rectangular pulse shape with controllable width and directionality will facilitate optimization of TMS as a probe of brain function and as a potential therapeutic intervention more closely matched to the physiology of the human brain. TMS holds promise for studying and treating psychiatric and neurological illnesses such as depression and schizophrenia, but its effectiveness has been constrained in part by device limitations. The proposed electronic device expands the functionality of this technique, helping to bring its substantial clinical therapeutic potential to fruition. [unreadable] [unreadable] [unreadable]